This invention relates generally to engine mounting systems which isolate vibration between a combustion-type engine and a support frame, and more particularly to a model airplane engine isolation and mounting system.
As the model aviation field has grown, both the aircraft design and the model airplane engines themselves have become more sophisticated and refined. This refinement has led to larger model aircraft and associated combustion-type model engines, as well as significantly more sophisticated radio, transmitter and receiver equipment.
Typically, the model aircraft itself is fabricated of either balsa wood and hardwood or a molded fiberglass air frame. In either event, delicate receiver and servo equipment are mounted within the air frame itself. Although elastomeric grommets are utilized in mounting the servos, and the receiver is wrapped in protective foam before installation, nonetheless larger combustion-type engines, both 2- and 4-stroke versions, generate significant vibration throughout the air frame when bolted directly to an upright fire wall thereof. Transmittal of these combustion and rotational vibrations are transmitted directly into the air frame because, in most instances, the only thing separating the engine and air frame fire wall is a one or two-part rigid engine mount.
An additional detrimental effect of transmitting engine vibration into the air frame is that glue joints and other bolt-on type equipment can be induced to fatigue, failure or disengagement. Hinges and actuating linkages for movable surfaces are also at risk from engine vibration and combustion harmonics. Additionally, and very importantly, noise, the loud drumming sound created by vibration transmitted throughout the model aircraft, has become a significant problem as noise limitations are currently being adapted and enforced at almost all model aircraft flying sites.
A number of devices have been introduced into the marketplace which, by their claims, afford some level of engine vibration isolation. However, many of these presently available model engine mounting systems have at least one of several failings. First, not all modes of vibration output from the model engine are adequately absorbed and isolated. Fore and aft forces are generated in the form of engine thrust through the propeller. Additionally, rotational torque and combustion harmonics inputs are also induced into the air frame, as well as lateral shear movement in all directions orthogonal to the axis of the engine.
A second failing of many of the present mounting systems available is that the engine/engine mounts are not captively connected to the air frame which could result in the rather violent disconnection between model engine and airplane when under power.
Yet another failing of some of the presently available systems is the difficulty with their installation. Some mounting systems require very accurate cutting and/or machining of the components to suit each environment. Almost all require that access be had to the rearward or inward side of the fire wall on an ongoing basis to effect installation, tightening and removal of the associated mounting hardware.
One such presently available system is manufactured by Gator R/C Products, Inc. of Pensacola, Fla. which provides two forms of its SOFT-N-SAFE model engine mounting system. One form is a radial mounting system providing a radial mounting plate which boltably connects to the existing back plate area of the model engine. The other form of this device provides a separate engine mount which boltably connects between engine and fire wall. Both embodiments provide a unique ISO-DAMP one-piece ribbed grommet having special serrations disposed against the fire wall surface and opposing spaced washer. The SOFT-N-SAFE mounting system does provide a captive arrangement, and does appear to afford fore and aft vibration isolation, but does very little to absorb both rotational harmonic and lateral shear engine vibration and movement.
Another device of which applicant is aware is the SOFT MOUNT model engine mounting systems provided by Software Associates of Houston, Tex. This mounting system, which is connectable between a conventional rigid engine mount and the fire wall of the air frame, provides a unique combination of mating elongated channel sections, one of which is U-section and houses a pair of conventional Lord-type cylindrical elastomer mounts, the other mating channel being L-shaped in cross section and connected between the exposed end of the elastomer mounts and the fire wall. The SOFT MOUNT places the elements in compression and shear and appears to provide a limited captive feature by virtue of a rigid inner sleeve bonded centrally within each of the Lord-type elastomeric mounts. Assembly and disassembly is cumbersome at best.
Sullivan Products of Baltimore, Md. also provides a model engine mount system which includes a special mounting plate interconnectable between engine back plate and conventional Lord-type mounts to blind nuts mounted on the back or inner surface of the fire wall.
An ISO-MOUNT system by Davis Diesel Development of Milford, Conn. is also presently being marketed which incorporates a conventional array of disc-shaped rubber isolators interconnectable between a specially configured engine mount and the air frame fire wall. This system also incorporates a conventional collapsible tubular T-nut which deforms to connect into a mating hole in the fire wall to facilitate later removal and re-installation of the system.
Applicant is also aware of the VEND MOUNT which provides inner and outer shouldered rubber grommets which are inserted through a suitable hole formed in the fire wall from either side thereof. A conventional fastener then clampably connects engine mount to fire wall via this split grommet arrangement.
The present invention provides a uniquely configured split grommet arrangement in combination with a split spool arrangement and a cooperatively structured rigid engine mount which may be either one or two part, the invention is easily boltable to a fire wall utilizing conventional blind nuts permanently positioned on the inner or rearward surface of the fire wall. All modes of vibration are effectively absorbed by this invention while providing a fully captive structure to prevent loss of engine control.